1. Technical Field
The present disclosure relates generally to a wound dressing for treating an open wound with a vacuum wound therapy treatment. In particular, the disclosure relates to a dressing having a cover layer employing a plurality of zones of variable performance characteristics to promote healing of the wound.
2. Background of Related Art
The body's natural wound healing process is a complex series of events beginning at the moment of injury. Initially the body reacts by delivering proteins and other factors to the wound through the blood stream to minimize the damage. Blood clots to prevent blood loss while cells engulf bacteria and debris to carry it away from the wound site. Next, the body begins to repair itself in a stage of healing often referred to as the proliferate phase. This phase is characterized by the deposition granulation tissue in the wound bed. Granulation tissue provides a base structure over which cells may migrate inwardly from the periphery to close the wound. Finally the process ends as collagen gives strength to new tissue over time often forming a scar.
One technique for promoting the natural healing process, particularly, but not exclusively during the proliferate phase, is known as vacuum wound therapy (VWT). Application of a reduced pressure, e.g. sub-atmospheric, to a localized reservoir over a wound has been found to assist in closing the wound. The reduced pressure may be effective to promote blood flow to the area to stimulate the formation of granulation tissue and the migration of healthy tissue over the wound in the natural process. Also a reduced pressure may assist in removing fluids exuding from the wound, which may inhibit bacterial growth. This technique has proven effective for chronic or non-healing wounds, but has also been used in for other purposes such as post-operative wound care.
The general VWT protocol provides for the introduction of a filler material into the wound to absorb exudates. The filler material may comprise such materials as non-reticulated foams, non-woven fabrics or gauze. The wound and the filler material may then covered by moisture vapor permeable cover layer that permits oxygen exchange with the environment, which may be essential for wound healing. The cover layer often includes an adhesive periphery that forms a substantially fluid tight seal with the healthy skin surrounding the wound. The cover layer thus defines a vacuum reservoir over the wound where a reduced pressure may be maintained over time by individual or cyclic evacuation procedures.
An aspect of concern in a VWT treatment is the management of forces generated in the dressing when a vacuum is applied. Such forces may cause the separation of the dressing from the skin, thereby limiting the effect of the VWT treatment and increasing the probability that microorganisms will infect the wound. Also, such forces may damage newly forming granulation tissue. The application of a vacuum can deform a flexible cover layer such that it compresses the filler and increases its tendency to adhere to the wound bed. Additionally, the deformation of the cover layer creates transverse shear forces along the skin-adhesive interface at the peri-wound area. These shear forces can cause the dressing to shift and/or pull away from the skin where gaps and wrinkles may develop. Such movement, and the mentioned results thereof, can inhibit the dressing's ability to provide a seal that is suitable for both the maintenance of a vacuum and for prohibiting the infiltration of contamination.
Adhesives applied to a cover layer to strengthen or reinforce the dressing's attachment to the skin may diminish the moisture vapor permeability of the dressing affecting its ability to permit oxygen exchange with the environment. Diminished moisture vapor permeability could also lead to the accumulation of moisture at the skin-adhesive interface. Permitting such an accumulation undermines the dressing's adhesion to the skin at the peri-wound area, thereby reducing the wear-time of the dressing, the effectiveness of the treatment and the health of the peri-wound area. Accordingly a need exists for a dressing suitable for use in a VWT procedure.